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United States Patent |
5,599,956
|
Pujado
,   et al.
|
February 4, 1997
|
Integrated process for the production of propylene oxide
Abstract
Propylene oxide may be produced by an integrated process utilizing as a
basic feedstock a refinery stream containing saturated hydrocarbons. The
first element of the process converts one or more of the saturated
hydrocarbons to a stream containing propylene and hydrogen using steam
cracking, catalytic cracking, or preferably catalytic dehydrogenation.
Hydrogen and propylene are separated, and the hydrogen is employed in a
reaction cycle affording hydrogen peroxide. The latter is then used to
epoxidize propylene in the presence of a suitable catalyst, especially a
titanosilicate.
Inventors:
|
Pujado; Peter R. (Palatine, IL);
Hammerman; John I. (Arlington Heights, IL)
|
Assignee:
|
UOP (Des Plaines, IL)
|
Appl. No.:
|
606108 |
Filed:
|
February 22, 1996 |
Current U.S. Class: |
549/531 |
Intern'l Class: |
C07D 301/12; C07D 303/04 |
Field of Search: |
549/531
|
References Cited
U.S. Patent Documents
5166372 | Nov., 1992 | Crocco et al. | 549/531.
|
5214168 | May., 1993 | Zajacek et al. | 549/531.
|
5221795 | Jun., 1993 | Clerici et al. | 549/531.
|
5354875 | Oct., 1994 | Nemeth et al. | 549/531.
|
5384418 | Jan., 1995 | Zajacek et al. | 549/531.
|
5463090 | Oct., 1995 | Rodriguez et al. | 549/531.
|
Primary Examiner: Evans; Joseph E.
Attorney, Agent or Firm: McBride; Thomas K., Snyder; Eugene I.
Claims
What is claimed is:
1. An integrated process for the production of propylene oxide from
saturated hydrocarbons comprising:
a. producing from a saturated hydrocarbon-containing feedstock a product
stream containing propylene and hydrogen;
b. separating said product stream into a propylene-rich stream and a
hydrogen-rich stream;
c. processing hydrogen in the hydrogen-rich stream in a peroxidation zone
at peroxidation conditions to obtain hydrogen peroxide;
d. epoxidizing in an epoxidation zone the propylene in the propylene-rich
stream with hydrogen peroxide in the presence of an epoxidation catalyst
at epoxidation conditions to form propylene oxide; and
e. recovering the propylene oxide formed.
2. The process of claim 1 where formation of the product stream is effected
by dehydrogenation of a propane-containing stream.
3. The process of claim 1 where formation of the product stream is effected
by steam cracking.
4. The process of claim 1 where formation of the product stream is effected
by catalytic cracking.
5. The process of claim 4 where formation of the product stream is effected
by fluid catalytic cracking.
6. The process of claim 1 where hydrogen peroxide is produced by
autoxidation of 2-alkylanthrahydroquinones.
7. The process of claim 1 where the epoxidation catalyst is a
titanosilicate.
8. The process of claim 7 where the titanosilicate is a titania-supported
titanosilicate.
9. The process of claim 1 where the propylene is epoxidized with hydrogen
peroxide and the reaction solution contains hydrogen peroxide at a
concentration not more than about 10 weight percent.
10. The process of claim 1 further characterized in that an external
hydrogen stream supplements the hydrogen-rich stream in the peroxidation
zone.
Description
FIELD OF THE INVENTION
This invention relates to the production of propylene oxide from propylene.
More particularly, our invention relates to an integrated process for the
production of propylene oxide by peroxidic oxidation of propylene where
the propylene itself is formed from one or more paraffins or paraffinic
streams typically found in refineries.
BACKGROUND OF THE INVENTION
Propylene oxide is an important article of commerce finding use in diverse
areas. For example, polymerization with alcohols as initiators affords
polyether polyols. Polymerization catalyzed by, e.g., ferric chloride
affords poly(propylene oxide) polymers with molecular weights of 100,000
or more. Reaction with water gives a spectrum of propylene glycols,
including monopropylene glycol, dipropylene glycol, tripropylene glycol,
and so forth. Reaction with ammonia, or amines generally, affords
aminoalcohols. Each of the foregoing are important niche commodities,
either per se or as reactive components in, e.g., polyurethane
manufacture.
The principal route to propylene oxide employs the so-called chlorohydrin
process where propylene is first convened to its chlorohydrin and the
latter is subsequently dehydrochlorinated to produce the epoxide.
Chlorohydrin formation is effected by reaction of aqueous chlorine or
hypochlorous acid with propylene under acidic conditions.
Dehydrochlorination is accomplished by treating the chlorohydrin with a
base.
More recently the oxidation of propylene with peroxide has become
competitive to the traditional chlorohydrin route. In addition to hydrogen
peroxide, organic peroxides may be used as the oxidant and include
materials such as t-butyl hydroperoxide, t-pentyl hydroperoxide,
ethylbenzene hydroperoxide, cumene hydroperoxide and peracetic acid. Where
organic peroxides are used an organic byproduct necessarily is formed. For
example, if t-butyl hydroperoxide is used as the oxidant t-butyl alcohol
is an unavoidable byproduct and any process using this organic
hydroperoxide must either find t-butyl alcohol as an economically
acceptable byproduct, (i.e., its market must make the overall process
economically viable) or the process must provide for recycling t-butyl
alcohol to t-butyl hydroperoxide. Epoxidation catalysts generally are
soluble metal compounds of, e.g., molybdenum, vanadium, tungsten, and
titanium.
Although the use of hydrogen peroxide as the oxidant would be singularly
advantageous, since its byproduct is water whose recycle is unnecessary,
until recently commercial routes to propylene oxide have focused on the
use of organic peroxides, such as t-butyl hydroperoxide and ethylbenzene
hydroperoxide, and commercially successful processes based thereon have
been developed. Even though the use of hydrogen peroxide as an oxidant has
many attractions, one limitation is the practical need for having a
hydrogen peroxide generation facility at the site, i.e., it is not
commercially feasible to transport large amounts of dilute hydrogen
peroxide to the oxidation site and the transport of concentrated solutions
presents safety hazards. Commercial generation of hydrogen peroxide is
merely the reaction of hydrogen and oxygen, although performed indirectly
rather than directly. Therefore, hydrogen peroxide generation requires a
source of hydrogen. Consequently, if one wishes to oxidize propylene with
hydrogen peroxide it is necessary that the complex have a continual and
guaranteed on-site source of hydrogen. We have recognized that the
foregoing conditions can be met if propylene is formed with the
coproduction of hydrogen, and that an integrated process can be devised
making propylene oxide production via peroxide-based oxidation of
propylene a commercial reality. The remainder of this application is
devoted to a description of our invention.
SUMMARY OF THE INVENTION
Our invention is an integrated process starting with various typical
refinery feeds for the production of propylene oxide via epoxidation using
hydrogen peroxide. An embodiment comprises converting a paraffinic
feedstream to a product stream containing hydrogen and propylene,
utilizing the separated hydrogen in the formation of hydrogen peroxide and
utilizing the separated propylene as a reactant in epoxidation with
hydrogen peroxide. In a more specific embodiment the propylene/hydrogen
product stream arises from catalytic dehydrogenation of propane. In
another embodiment the reaction of hydrogen peroxide and propylene is
catalyzed by a titanium silicalite. Other embodiments will appear from the
following description.
DESCRIPTION OF THE FIGURES
FIG. 1 is a simplified flow diagram for the integrated process of our
invention.
DESCRIPTION OF THE INVENTION
The invention herein is an integrated process using a common refinery feed
to ultimately produce propylene oxide with minimal byproduct formation
other than those products normally found in a refinery. Our invention is
concisely summarized in FIG. 1. The remainder of this application will
elaborate upon the integrated process, its elements, and various
embodiments thereof. Our integrated process clearly provides three
distinct elements. The first may be termed the propylene production unit
and is characterized by conversion of one or more paraffins, generally
part of a typical refinery stream, to a product containing propylene and
hydrogen. By suitable separation processes the product stream is purified
to afford a hydrogen concentrate stream and a propylene rich stream. In
the second element of our invention hydrogen is reacted with oxygen,
albeit indirectly, to afford hydrogen peroxide. Whether the hydrogen
concentrate needs further purification prior to its use depends on many
factors and FIG. 1 accommodates and includes the possibility of further
hydrogen purification as a necessary or desirable adjunct incident to its
use in hydrogen peroxide production. The last element of our invention is
the catalytic epoxidation of propylene with hydrogen peroxide. Further
purification of propylene prior to its epoxidation may be desirable or
even required, although this is not generally contemplated, depending upon
its mode of production and the precise nature of the epoxidation.
The first element in our invention is propylene production from a saturated
hydrocarbon-containing feedstock, with accompanying formation of hydrogen
as a coproduct. There are three main methods of propylene formation in
this context; steam cracking, catalytic cracking and especially the
subclass of fluid catalytic cracking, and propane dehydrogenation. All
three of the foregoing methods share the characteristic that the reaction
product contains both propylene and hydrogen, which as stated previously
is a prerequisite of propylene production in our integrated process. See
Ullmann's Encyclopedia of Industrial Chemistry, 5th, Completely Revised
Edition, Vol. A22, pp. 213-220 (1993). The catalytic conversion of
methanol or dimethyl ether to olefins affords propylene and ethylene, but
no hydrogen.
Steam cracking is used primarily for the formation of ethylene but
propylene is a major byproduct. See op. cit., Vol. A10, pp. 47-61 (1987).
Stem cracking is essentially the pyrolysis of hydrocarbons in the presence
of stem. In stem cracking a hydrocarbon stream is heated and mixed with
stem to a temperature in the range of 500.degree.-650.degree. C. The
stream then enters a reactor where it is further heated to
750.degree.-875.degree., temperatures where saturated hydrocarbons in the
feedstock crack into smaller molecules. The overall reaction is highly
endothermic and is energy intensive. The feedstocks in steam cracking
generally contain straight and branched-chain alkanes as well as
naphthenes or cycloparaffins. Aromatics generally do not contribute to
cracked products, i.e., products of lower molecular weight, but often are
present in the feedstream which typically is produced elsewhere in a
refinery. Typical steam cracking feedstocks for propylene production range
from LPG to condensates or light naphthas. The naphtha feedstocks common
in stem cracking are composed largely of paraffins and cycloparaffins with
smaller amounts of aromatics. Gas oil is yet another example of a
feedstock which affords a product stream containing both propylene and
hydrogen.
A second method of producing propylene is via catalytic cracking; see op.
cit, Vol. A18, pp. 61-4 (1991). Chemically, catalytic cracking is
analogous to steam cracking in that it is essentially a pyrolytic
reaction. However, a catalyst enables cracking (pyrolysis) to occur at
lower temperatures, and consequently catalytic cracking is far less energy
intensive than steam cracking. Catalytic cracking is essentially the
conversion of paraffins and cycloparaffins to materials of lower molecular
weight and is characterized by cleavage of carbon-carbon and
carbon-hydrogen bonds.
Fluid catalytic cracking (FCC) is an especially important variant of
catalytic cracking processes and is the major commercial variant practiced
today. See "Handbook of Petroleum Refining Processes," Robert A. Meyers,
Editor, pp 2-9 to 2-32. The natural clays, such as montmorillonite,
originally used as catalysts were supplanted by various silica aluminas,
which in turn have been largely supplanted by zeolitic material. Certainly
the contemporary catalysts of choice in FCC are zeolites.
The third major method of propylene production is the catalytic
dehydrogenation of propane. See "Ullmann's Encyclopedia of Industrial
Chemistry," 5th, Completely Revised Edition, Vol. A22, pp 216-19 (1991).
Any method of propane dehydrogenation may be used and is largely a matter
of operator's choice. However, that variant known as the Oleflex.TM.
process is our preferred choice. See "Handbook of Petroleum Refining
Processes," Robert A. Meyers, Editor, pp 4-23 to 4-28.
In a typical hydrocarbon dehydrogenation process, the feed hydrocarbons
(both fresh feed hydrocarbons and recycled unconverted hydrocarbons) are
admixed with hydrogen and the resulting admixture is heated by indirect
heat exchange with the dehydrogenation reaction zone effluent. After being
heated in the feed-effluent heat exchanger, the feed stream is further
heated by passage through a heater which is typically a fired heater or
furnace. The admixture, typically referred to as the combined feed, is
then contacted with a bed of dehydrogenation catalyst, which may exist as
a fixed bed, a fluidized bed, or a movable bed via gravity flow. The
resulting dehydrogenation zone effluent is withdrawn from the reaction
zone and after indirect heat exchange with the combined feed, it is passed
to product separation facilities. Generally, the product separation
facilities are employed to produce a gas stream, comprising substantially
hydrogen, a portion of which may be recycled back to the catalytic
reaction zone to provide hydrogen for admixture with the hydrogenatable
hydrocarbon feed stream. Generally, a first product stream is produced
comprising the desired product olefins and a second product stream
comprising light hydrocarbons, typically known as light hydrocarbon
by-products, having fewer carbon atoms per molecule than the desired
product olefin. Both of these product streams may be recovered in the
product separation facilities. In addition, a recycle stream comprising
unconverted dehydrogenatable feed hydrocarbons may be withdrawn from the
product separation facilities and recycled back into the combined feed
stream. Fundamental to the catalytic dehydrogenation process is the fact
that the dehydrogenation reaction is highly endothermic which results, as
the reaction proceeds, in cooling the reactants to a temperature at which
the dehydrogenation reaction will not proceed at any appreciable rate. To
counteract this problem, additional heat must be supplied to the bed of
dehydrogenation catalyst to assure reaction rates sufficient to make a
commercial process economically feasible. Accordingly, many methods of
supplying this additional heat have been contrived in order to make
catalytic dehydrogenation a viable commercial process.
Many variants of catalysts have been used and are known, although the most
effective ones appear to be based on a supported zerovalent platinum or
palladium. A range of catalysts used in this process is summarized in U.S.
Pat. No. 4,886,928 and U.S. Pat. No. 4,914,075, both of which are hereby
incorporated by reference. Several processing variants also are available;
see U.S. Pat. No. 4,886,928 for a brief discussion.
The product stream from each of the foregoing processes typically contains
components other than propylene and hydrogen and the latter need to be
separated in an appropriate fashion. Many separation process variants are
available; see "Ullman's Encyclopedia of Industrial Chemistry," Vol. A22,
pp 214-6 for several separation techniques applied when the product stream
arises in a cracking process. U.S. Pat. No. 5,177,293 describes other
separation processes appropriate for the product stream arising in the
dehydrogenation of propane. Because recovery of a hydrogen concentrate
stream and a propylene rich stream from any of the three propylene
production methods discussed above is well known in the art, no detailed
description needs to be further elaborated upon.
The hydrogen formed in the propylene production unit is separated,
recovered, and purified where necessary for subsequent use in the
production of hydrogen peroxide. It is contemplated that the well-known
commercial methods of hydrogen recovery will suffice to afford a hydrogen
concentrate of sufficient purity for use in hydrogen peroxide manufacture,
but if additional purification is required or desired the skilled artisan
will know to employ many suitable methods, such as membrane purification,
pressure swing adsorption, and so forth. In any event hydrogen peroxide
will be produced by direct combination of molecular hydrogen and oxygen or
by reaction of molecular oxygen with various hydrogen-containing
compounds. The latter is by far the most preferred method of hydrogen
peroxide generation, especially when demand is steady and high.
The preferred process to produce hydrogen peroxide in the context of the
present invention is based on a reaction cycle comprising autoxidation of
2-alkylanthrahydroquinones. An alkylanthraquinone in solution is
catalytically hydrogenated to its corresponding alkylanthrahydroquinone,
which subsequently is aerated with an oxygen-containing gas to form
hydrogen peroxide and regenerate the alkylanthraquinone. The
2-alkylanthraquinone, for example 2-alkyl-9,10-anthracenediol or
2-alkylanthraquinol, generally is designated as the reaction carrier,
hydrogen carder or working material. The solvent for the reactants is
called the working solution, and may comprise one or more of alcohols,
The reaction carrier preferably is esters, caprolactams, ureas, amides and
pyrrolidones. hydrogenated over a palladium catalyst.
Favored industrial 2-antkraquinone carriers include 2-t-amylanthraquinone,
2-s-amylanthraquinone, 2-t-butylanthraquinone and 2-ethylanthraquinone.
During hydrogenation of the alkylanthraquinone to its corresponding
alkylanthrahydroquinone, the latter may undergo further reduction to a
tetrahydroalkylanthrahydroquinone. This compound releases hydrogen
peroxide with the formation of a tetrahydroalkylanthraquinone, which can
react with the alkylanthrahydroquinone to reform alkylanthraquinone plus
tetrahydroalkylanthrahydroquinone, i.e., in a parallel reaction sequence.
This latter sequence is a slower reaction, requiring higher temperatures,
which is significant in some commercial processes. Various byproducts of
the reactions build up in the working solution until purged.
The preferred palladium catalyst used in the hydrogenation reaction may be
supported on a carder as a slurry or fixed bed or used as palladium black,
wire screen or gauze. Slurry catalysts may be removed and rejuvenated or
replaced without a shutdown, but is burdened with suspension difficulties.
A fixed catalyst bed requires less stringent feed filtration and avoids
inflexibility associated with maintenance of suspension, but requires
periodic shutdowns for catalyst rejuvenation or replacement. Hydrogenation
operating conditions include a pressure of from about 0.2 to 0.5 MPa
absolute and a temperature of up to about 75.degree. C. Minimization of
the tetrahydroalkylanthraquinone reaction sequence is favored by lower
temperatures in about the 25.degree. to 40.degree. C range. Other
considerations in the product of hydrogen peroxide are outlined in, e.g.,
"Kirk Othmer Encyclopedia of Chemical Technology," Rev. 4, Vol. 13, pp
966-81.
The hydrogen peroxide used in epoxidation of propylene preferably is an
aqueous solution. Concentrations of hydrogen peroxide in the reactant
mixture typically are less than 10 weight percent, and even about 5 weight
percent hydrogen peroxide in the process stream is effective. That the
oxidation process is effective with a "working solution" containing under
10 weight percent hydrogen peroxide is quite advantageous and constitutes
one of the benefits derived from our invention. As to the relative amounts
of hydrogen peroxide and propylene, at a high efficiency of peroxide
utilization approximately equal molar amounts of hydrogen peroxide and
propylene are preferable. In the most usual case, from about 0.9 to about
1.1 molar proportions of hydrogen peroxide are used per mole of propylene.
However, the molar proportions of hydrogen peroxide to propylene may vary
between about 0.5 and 2, or even between about 0.2 and about 5.
The hydrogen peroxide as produced is reacted with propylene oxide under
epoxidation conditions in the presence of a suitable catalyst. Many
catalysts are known for this reaction, including molybdenum-based
catalysts. More recently titanosilicate catalysts have been reported to
operate quite effectively in the epoxidation of propylene with hydrogen
peroxide and they constitute the favored mode in the practice of our
integrated process. The use of titanosilicates as an epoxidation catalyst
for propylene has been described in U.S. Pat. No. 4,833,260.
More recently an improved titanosilicate, namely a titania-supported
titanosilicate, has been described in U.S. Pat. No. 5,354,875 as
particularly effective in catalyzing the conversion of propylene to
propylene oxide with hydrogen peroxide as the oxidant, especially where
the "working solution" (i.e., reactant mixture) contains under 10 weight
percent hydrogen peroxide. The materials described therein as catalysts
effect conversion of olefins in yields in excess of 90% and with virtually
100% efficiency of hydrogen peroxide utilization. However, it needs to be
emphasized that however preferable that particular mode of propylene
epoxidation is favored our invention subsumes all modes where hydrogen
peroxide serves as the oxidant and propylene is the reactant on which it
acts to produce propylene oxide.
FIG. 1 is a flow diagram for the integrated process of our invention and
represents some of the many variants which are possible. Although the
figure is largely self-explanatory we will give a brief description. The
feedstock entering the propylene production unit contains saturated
hydrocarbons, normally a mixture of straight and branched-chain alkanes
and also may contain naphthenes or cycloparaffins. The propylene
production unit itself is generally either a steam cracking unit, a
catalytic cracking unit, including an FCC unit, or a propane
dehydrogenation unit. The products include propylene, part of which may be
used for purposes outside the scope of this invention, other olefins, and
hydrogen. The hydrogen formed in the production of propylene is used as
one of the reactants, along with oxygen, in the hydrogen peroxide unit. As
indicated in our example, it is likely that the hydrogen accompanying the
formation of propylene is insufficient to make the requisite mount of
hydrogen peroxide necessary for the epoxidation of propylene, consequently
additional hydrogen needs to be imported. Some of the hydrogen peroxide
produced may be used independently, but it is contemplated that most, if
not all, of the hydrogen peroxide production will be used to oxidize
propylene in the propylene oxide unit. Water that accompanies the
epoxidation of propylene is returned from the propylene oxide unit to the
hydrogen peroxide unit and the product propylene oxide is recovered.
The following example is merely illustrative of our invention and is not
intended to restrict it in any way.
EXAMPLE 1
The following represents mass balances required for the production of
100,000 metric tons of propylene oxide. The theoretical amounts, given in
metric tons, assume 100% reaction. The actual amounts projected are based
on yields given in parentheses following the amounts.
TABLE 1
______________________________________
Requirements for Production of
100 Metric Tons of Propylene
Oxide
Theoretical.sup.a
Actual.sup.b
______________________________________
Propylene (100% pure)
72,452 73,931 (98%)
Hydrogen Peroxide (100% pure)
58,567 61,649 (95%)
To produce 100% pure H.sub.2 O.sub.2
requires
a) for 58,567 metric tons
H.sub.2 (100%) 3471 3951 (88%)
O.sub.2 55,096
b) for 61,649 metric tons
H.sub.2 (100%) 3654 4159 (88%)
To produce 100% pure propylene
requires
a) for 72,452 metric tons
propane (100%) 75,923 86,129 (88%)
H.sub.2 (100%) - net from
3471 2306
separation.sup.c
b) for 73,931 metric tons
propane (100%) 77,473 87,887
H.sub.2 (100%) - net from
3542 2353
separation.sup.c
______________________________________
.sup.a Amounts, in metric tons, for 100% utilization
.sup.b Amounts, in metric tons, for actual utilization based on yield or
conversion given in parentheses.
.sup.c Net pure hydrogen obtained after separation via pressure swing
adsorption.
This table shows that production of 100,000 metric tons of propylene likely
requires 61,649 metric tons H.sub.2 O.sub.2, which in turn requires about
4159 metric tons hydrogen. However, formation of 73,931 metric tons
propylene will afford only about 2,353 metric tons hydrogen. Consequently,
additional hydrogen will need to be furnished to the hydrogen peroxide
unit if all of the propylene produced is epoxidized. Of course, part of
the propylene produced may be diverted to other uses, in which case
additional hydrogen needs are reduced.
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